Indiums with indium halides

Allylation of acyloyl-imidazoles and pyrazoles61 with allyl halide mediated by indium in aqueous media provides a facile regioselective synthesis of P, y-unsaturated ketones (Scheme 11.1), which has been applied to the synthesis of the monoterpene artemesia ketone. The same product can be obtained by indium-mediated allylation of acyl cyanide (Eq. 11.35).62 Samarium, gallium, and bismuth can be used as a mediator for the allylation of nitrones and hydrazones to give homoallylic hydroxylamine and hydrazides in aqueous media in the presence of Bu4NBr (Scheme 11.2).63 The reaction with gallium and bismuth can be increased dramatically under microwave activation. 

Reaction with Propargyl Halides. The indium-mediated coupling of propargyl bromide with a variety of imines and imine oxides afforded homo-propargylamine derivatives in aqueous media under mild conditions.78 Propargylation of glyoxylic oxime ether in the presence of a catalytic amount of palladium(O) complex and indium(I) iodide in aqueous media was also studied (Eq.11.47).79... 

Scheme 1. Reactions of indium halides with l,3-diisopropyl-4,5-dimethylimidazol-2-yhdene.

A third route to allenyltin halides involves transmetallation of isolable allenyltri-butyltin compounds, as exemplified by the reaction of allenyltributyltin with Bu2SnCl2 [68]. The resulting mixture of allenyl- and propargyldibutyltin chlorides reacts with various aldehydes to afford mixtures of propargyl- and allenylcarbinols (Eqs. 9.78 and 9.79). The yields of these additions are uniformly high, but the selectivity depends on the nature of the aldehyde substituent. The transmetallation route to allenyltin and -indium halides will be discussed in more detail in a later section. 

In contrast to the non-trivial routes for the syntheses of pure aluminum(I) or gallium(I) subhalides, indium(I) chloride or bromide can simply be prepared by melting mixtures of elemental indium and indium trihalides [39]. When these in-dium(I) halides were treated with bulky alkyllithium compounds, deep violet orga-noelement indium dusters (13-18) were obtained [Eq. (3)] [40, 41]. 

As for the synthesis of ort/io-phenylene indium complexes, the transmetallation reactions of organomercurials with indium(I) halides have also been considered for the preparation of 1,8-naphthalenediyl diindium complexes. While the dimercura-cycle 62 fails to react with InBr, l,8-bis(chloromercurio)naphthalene (25) and 1,8-bis(bromomercurio)naphthalene (63) react with their respective indium(I) halides to yield the mercura-indacycles 64 and 65 (Scheme 25) which have been isolated as bis(THF) adducts. The indium center of 65-(THF)2 is penta-coordinated and... 

As with indium, the literature contains a number of surveys of the general inorganic1 and organometallic chemistry of thallium,273 and the reviews of this element already cited are also concerned with the adducts of the halides and pseudohalides,5 and with other aspects of the coordination chemistry.6 A monograph by Lee provides a most useful treatment of the literature up to 1970.274 The application of thallium compounds in organic synthesis has been discussed.275 276... 

All the above complexes, 9-12, are isolated from reactions involving gallium or indium metal and [Mn2(CO)10] or [Re2(CO)10] in an autoclave, although 11 has also been obtained by thermolysis of 6. Some details on the reactivity of 11 toward phosphonium halides (23) have been reported and indicate formation of the halo-indium complexes [PPh4]2[Mn2(CO)8 /j-lnX2 2]. A higher nuclearity cluster has also been obtained in the reaction of [Re2(CO)10] with indium metal, viz. [Re4(CO)12 /i3-InRe(CO)5 4], 13 (24,24a). This consists of a central tetrahedral Re4(CO)12 core with each face capped by an InRe(CO)s fragment as shown in Fig. 4. 

A three-component reaction based on the umpolung of re-allylpalladium (II) complexes indium metal was reported by Grigg and co-workers (Scheme 8.31) [74]. In this reaction, the electrophilic nature of the n-allyl palladium species generated from aryl halides and allenes is reversed by transmetallation with indium metal. The resultant nucleophilic allylindium reagent subsequently adds to the third component - aldehyde [75] or imine [76] - to give the corresponding homo-allylic alcohol 64 or amine 65 respectively. 

Benzyl methyl ether or allyl methyl ethers can be selectively metalated at the benzylic/allylic position by treatment with BuLi or sBuLi in THF at -40 °C to -80 C, and the resulting organolithium compounds react with primary and secondary alkyl halides, epoxides, aldehydes, or other electrophiles to yield the expected products [187, 252, 253]. With allyl ethers mixtures of a- and y-alkylated products can result [254], but transmetalation of the lithiated allyl ethers with indium yields y-metalated enol ethers, which are attacked by electrophiles at the a position (Scheme 5.29). Ethers with ft hydrogen usually undergo rapid elimination when treated with strong bases, and cannot be readily C-alkylated (last reaction, Scheme 5.29). Metalation of benzyl ethers at room temperature can also lead to metalation of the arene [255] (Section 5.3.11) or to Wittig rearrangement [256]. Epoxides have been lithiated and silylated by treatment with sBuLi at -90 °C in the presence of a diamine and a silyl chloride [257]. 

The coupling reaction of a-keto esters with allyl, propargyl, and allenyl halides using indium metal in aqueous solvents affords a-hydroxy-y,<5-unsaturated esters (Equation (28)).197,198 1,3-Dicarbonyl compounds undergo efficient carbonyl allylation reactions in an aqueous medium through a Barbier-type reaction (Equation (29)). The reaction is general and a variety of 1,3-dicarbonyls has been alkylated using allyl bromide or allyl chloride in conjunction with indium.199... 

Treatment of tethered alkyne-allyl halides with indium metal in halogenated solvents affords carbocyclic vinyl halides via a novel atom-transfer reaction. The reactions are operationally facile and proceed smoothly at room temperature even with sub-stoichiometric quantities of indium. Use of a halogenated solvent containing a different... 

The alkenylindium compounds, obtained by the addition of benzyl- and allylindium to alkynes, couple with organic halides in the presence of a palladium catalyst to give the three-component coupling products (Scheme 99).286 1,3-Dibromopropene or 3-bromo-l-iodopropene reacts with indium to give diindiopropene 87a,b.147,148 This dimetallic reagent reacts with two different electrophiles successively carbonyl compounds and imines are allowed to react with 87 as the first electrophile to give vinylic indium intermediates 88, which react with... 

Highly regioselective radical addition of the indium hydride reagent HInCl2 to alkynes has been achieved. Various functionalities are tolerant under the reaction conditions. The reaction proceeds with complete // -stereoselectivity. Alkenylindium compounds obtained by this hydroindation can be employed for the subsequent cross-coupling reactions with aryl halides in one pot (Scheme 109).374,375... 

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